bearSSL clientSecure initial heap usage

[kapyaar]

Basic Infos

• This issue complies with the issue POLICY doc.
• I have read the documentation at readthedocs and the issue is not addressed there.
• I have tested that the issue is present in current master branch (aka latest git).
• I have searched the issue tracker for a similar issue.
• I have filled out all fields below.

Platform

• Hardware: [ESP-12]
• Core Version: [latest git]
• Development Env: [Arduino IDE]
• Operating System: [Windows]

Settings in IDE

• Module: [Nodemcu]
• Flash Mode: [DOUT]
• Flash Size: [4MB/1MB]
• lwip Variant: [v2 Lower Memory]
• Reset Method: [nodemcu]
• Flash Frequency: [40Mhz]
• CPU Frequency: [80Mhz]
• Upload Using: [SERIAL]
• Upload Speed: [921600)

Problem Description

When Using BearSSL secureClient, there is about 4k heap that gets taken up that does not get released. Is this normal?

I am using the latest git version, and I updated the bearSSL files based on #4900

When getting started, heap is 48504. This falls to some 43900 and it says there. I have a case where with a project, this 4k becomes significant as the ESP crashes due to low heap.

MCVE Sketch

// Example of the different modes of the X.509 validation options
// in the WiFiClientBearSSL object
//
// Mar 2018 by Earle F. Philhower, III
// Released to the public domain

#include <ESP8266WiFi.h>
#include <time.h>

const char *ssid = "myWiFiSSID";
const char *pass = "myWiFiPassword";

const char *   host = "api.github.com";
const uint16_t port = 443;
const char *   path = "/";


// Try and connect using a WiFiClientBearSSL to specified host:port and dump HTTP response
void fetchURL(BearSSL::WiFiClientSecure *client, const char *host, const uint16_t port, const char *path) {
  if (!path) {
    path = "/";
  }

  Serial.printf("Trying: %s:443...", host);
  client->connect(host, port);
  if (!client->connected()) {
    Serial.printf("*** Can't connect. ***\n-------\n");
    return;
  }
  Serial.printf("Connected!\n-------\n");
  client->write("GET ");
  client->write(path);
  client->write(" HTTP/1.0\r\nHost: ");
  client->write(host);
  client->write("\r\nUser-Agent: ESP8266\r\n");
  client->write("\r\n");
  uint32_t to = millis() + 5000;
  if (client->connected()) {
    do {
      char tmp[32];
      memset(tmp, 0, 32);
      int rlen = client->read((uint8_t*)tmp, sizeof(tmp) - 1);
      yield();
      if (rlen < 0) {
        break;
      }
      // Only print out first line up to \r, then abort connection
      char *nl = strchr(tmp, '\r');
      if (nl) {
        *nl = 0;
        Serial.print(tmp);
        break;
      }
      Serial.print(tmp);
    } while (millis() < to);
  }
  client->stop();
  Serial.printf("\n-------\n\n");
}



void fetchInsecure() {
  BearSSL::WiFiClientSecure client;
  client.setInsecure();
  fetchURL(&client, host, port, path);
}








void setup() {
  Serial.begin(115200);
  Serial.println();
  Serial.println();

  // We start by connecting to a WiFi network
  Serial.print("Connecting to ");
  Serial.println(ssid);
  WiFi.mode(WIFI_STA);
  WiFi.begin(ssid, pass);

  while (WiFi.status() != WL_CONNECTED) {
    delay(500);
    Serial.print(".");
  }
  Serial.println("");

  Serial.println("WiFi connected");
  Serial.println("IP address: ");
  Serial.println(WiFi.localIP());
}


void loop() {
  Serial.print( F("Heap Before: ") ); Serial.println(ESP.getFreeHeap());
  fetchInsecure();
  Serial.print( F("Heap After: ") ); Serial.println(ESP.getFreeHeap());
  delay(5000);
}

Debug Messages

SDK:3.0.0-dev(c0f7b44)/Core:win-2.5.0-dev/lwIP:2.0.3(STABLE-2_0_3_RELEASE/glue:arduino-2.4.1-13-g163bb82)/BearSSL:6d1cefc


Connecting to myWiFiSSID
bcn 0
del if1
usl
mode : sta(5c:cf:7f:aa:bd:06)
add if0
.....scandone
state: 0 -> 2 (b0)
.state: 2 -> 3 (0)
state: 3 -> 5 (10)
add 0
aid 1
cnt 

connected with myWiFiSSID, channel 1
sec 3ff error
dhcp client start...
.........ip:192.168.254.59,mask:255.255.255.0,gw:192.168.254.1
.
WiFi connected
IP address: 
192.168.254.59
**Heap Before: 48504**
Trying: api.github.com:443...Connected!
-------
HTTP/1.1 403 Forbidden
-------

Heap After: 43912
pm open,type:2 0
Heap Before: 43424
Trying: api.github.com:443...Connected!
-------
HTTP/1.1 403 Forbidden
-------

Heap After: 43424
Heap Before: 43424
Trying: api.github.com:443...Connected!
-------
HTTP/1.1 403 Forbidden
-------

[earlephilhower]

This is expected. BearSSL, when used, needs ~4.5KB of RAM as a private stack. It's allocated as soon as a BearSSL connection object is instantiated. Note, however, only a single 4.5K stack is needed no matter how many connections you use, so it's a 1-time payment.